1. Field of the Invention
The present invention relates to an automatic buttonholing apparatus in a zigzag sewing machine. More specifically, the present invention relates to an automatic buttonholing apparatus in a zigzag sewing machine using a separate attachment in buttonholing.
2. Description of the Prior Art
FIG. 1 is a diagram showing one example of a buttonhole depicting the background of the invention. As shown, bar tack portions 21 and 22 are formed at upper and lower ends of a buttonhole 1. The left side 23 and the right side 24 of the buttonhole 1 are hemstitched with a predetermined width completing the buttonhole. During buttonholing, it is necessary to fix an attachment such as a cloth present (not shown in FIG. 1).
FIG. 2 is a perspective view showing a buttonhole guide foot portion which constitutes the background of the invention. The buttonhole guide foot comprises a U-shaped shoe 3 and a presser foot 4. The pressure foot 4 comprises a shank 6 fixed to a presser bar 5 by means of a screw 6a and a sliding foot 7 such as a plastic foot pivoted to the shank 6, wherein the sliding foot 7 is loosely and slidably inserted into the shoe 3. A needle plate 10 having a needle hole 9 for thrusting of a needle 8a mounted to a needle bar 8 is positioned at the lower portion of the shoe 3. The attachment for pressing a cloth being buttonholed is thus provided; however, since such a buttonhole guide foot is already well-known a more detailed description will be omitted.
With such a conventional zigzag sewing machine as described above, it is required that buttonholing need be effected after the attachment, i.e. the cloth presser is mounted to the pressing bar. On the other hand, such a zigzag sewing machine is provided with a selection switch, not shown, for selecting a buttonholing mode or a pattern sewing mode, such as a general straight stitch, zigzag or superzigzag pattern. If it is desired to sew in a straight line, a selection button is depressed for straight stitch. Then a bight (a swinging width)and a feed (a cloth feed) for straight stitch are set in the sewing machine. The same applies to sewing of other zigzag patterns. If it is desired to make a buttonhole, the machine operator actuates a selection button for buttonholing. However, in the absence of a cloth presser as shown in FIG. 2, buttonholing as shown in FIG. 1 cannot be achieved. Accordingly, it is necessary to affix such an attachment when the selection switch for buttonholing is operated. In other words, if and when the sewing machine is operated, with such cloth presser provided, by operating the pattern selection switch, a sewing needle may come into contact with a portion of the cloth presser on a seam may become improper. Accordingly, it is necessary to force an operator to affix the attachment during buttonholing and conversely to remove the attachment during pattern sewing.